Circuit arrangement for charging a storage capacitor

ABSTRACT

A first pair of antiparallel connected thyristors are connected in series with the a.c. input and the primary of a transformer. These thyristors are ignited respectively at the start of each half cycle. A rectifier is connected across the transformer secondary and across the storage capacitor to be charged. An auxiliary capacitor in series with a resistor are connected across the a.c. input. A second pair of antiparallel thyristors have an ignition device. The latter ignition device is controlled by a voltage derived from a voltage divider across the storage capacitor and ignite the second pair of thyristors some time after the start of successive half cycles. When ignited the respective second thyristor applies the voltage of the auxiliary capacitor across the first pair of thyristors in opposition to the a.c. voltage thereacross to turn off the ignited thyristor of the first pair.

United States Patent 1 Ludloff [54] CIRCUIT ARRANGEMENT FOR CHARGING ASTORAGE CAPACITOR [75] Inventor: Wolfgang Ludloff, Porz-Westhoven,

Germany [73] Assignee: Multiblitz Dr. Ing. D. A. Mannesmann GmbII, & Co.KG., Porz- Westhoven, Germany [22] Filed: May 4, 1972 [21] App1.No.:250,379

. [30] Foreign Application Priority Data 315/194, 219, 223, 229, 232,233, 308, 311, l00 S; 307/252 T, 297; 323/22 SC, 24, 25

1451 Mar. 27, 1973 FOREIGN PATENTS OR APPLICATIONS 895,529 3/1972 Canada..323/22 SC Primary ExaminerGerald Goldberg Att0rneyl-Ioward H. Darbo eta1.

[57] ABSTRACT A first pair of antiparallel connected thyristors areconnected in series with the a.c. input and the primary of atransformer. These thyristors are ignited respectively at the start ofeach half cycle. A rectifier is connected across the transformersecondary and across the storage capacitor to be charged. An auxiliarycapacitor in series with a resistor are connected across the a.c. input.A second pair of antiparallel thyristors have an ignition device. Thelatter ignition device is controlled by a voltage derived from a voltagedivider across the storage capacitor and ignite the second pair ofthyristors some time after the stafl: of successive half cycles. Whenignited the respective second thyristor applies the voltage of theauxiliary capacitor across the first pair of thyristors in opposition tothe a.c. voltage thereacross to turn off the ignited thyristor of thefirst pair.

8 Claims, 1 Drawing Figure [56] References Cited UNITED STATES PATENTS3,490,030 1/1970 Kelley, Jr ..323/24 SC 3,643,405 2/1972 Vukasovic etal. ..323/22 SC I l i CIRCUIT ARRANGEMENT FOR CHARGING A STORAGECAPACITOR BACKGROUND AND SUMMARY OF THE INVENTION This invention relatesto a circuit arrangement for charging a storage capacitor to anadjustable voltage by means of a rectified a.c. voltage. Circuitarrangements of the type indicated can, for instance, be used in orderto charge a storage capacitor for a flash unit to an adjustable voltage,the storage capacitor discharging via an electron flash tube asindividual flash or as stroboscopic flashes.

It is prior art to charge the storage capacitor via a thyristor circuit,the control of the voltage being effected by a firing angle control(phase control). In such prior art circuit arrangements the firing anglecontrol must take place during the decreasing quarter-period of eachhalf-wave, since were the firing angle control operative in theincreasing part of the half-wave, the capacitor voltage would rise viathe rectifier to the maximum value of the a.c. voltage'at any event.Upon ignition of the thyristor, the voltage must then rise very rapidlyto the instantaneous value of the applied a.c. voltage. Thus, the a.c.voltage is practically applied in short-circuit across the emptycapacitor via the thyristor. Thereby, a high current pulse is obtainedwhich loads the construction elements accordingly. A furtherdisadvantage is that the point of ignition is connected according to asine function with the desired voltage value so that means must beprovided in order to vary the point of ignition according to an inversesine function of the desired capacitor voltage.

It is an object of this invention to so design a circuit arrangement forcharging a storage capacitor so that no undesired high current pulsesoccur and the adjustment of the desired capacitor voltagecan be effectedin a simple manner. According to the invention, this object is attainedby providing that a first pair of antiparallelly connected thyristorsare connected in the a.c. circuit which thyristors are ignited by afirst ignition circuit during the zero passages of the alternatingcurrent, that a capacitor is charged by the a.c. voltage in eachhalfwave via a charging resistor, and that a second pair ofantiparallelly connected thyristors are provided which are ignited by asecond ignition circuit and via which the capacitor voltage is appliedacross the thyristors of the first pair in opposition to the a.c.voltage thereacross.

In contrast to a firing angle control the thyristors of the first pairare ignited at the beginning of each halfwave. Now a gradual charge ofthe capacitor in response to the voltage increasing in this half-wavetakes place. Thus, the capacitor need not be charged suddenly to theinstantaneous value of the a.c. voltage. If the instantaneous value ofthe a.c. voltage and therewith the voltage of the storage capacitor hasreached the desired value, the respectively ignited thyristor of thefirst pair will be quenched by means of a thyristor of the second pairapplying the capacitor voltage of the auxiliary capacitor across thethyristor of the first pair in opposition to the a.c. voltagethereacross. As the auxiliary capacitor is also charged substantially tothe instantaneous value of the a.c. voltage, in this manner the voltagedrop across the ignited thyristor of the first pair becomes zero, sothat this thyristor is quenched. Therewith the charge of the storagecapacitor is terminated.

The invention offers the possibility of controlling the second ignitioncircuit by the voltage across the storagecapacitor. Since the storagecapacitor is charged until a given desired value is reached and then thecharging is interrupted from this value via the second ignition circuit,it is not necessary to convert the voltage setpoint value according toan inverse sine function to a phase shift for the ignition pul'se.

The invention can be realized in such a manner that an adjustablevoltage divider is connected in parallel to the storage capacitor andthe partial voltage picked off across the voltage divider controls theignition circuit for the second (or quenching) pair of thyristors via acircuit element having a threshold value, such as a glow lamp.

It is furthermore advantageous if the a.c. voltage is connected to arectifier bridge via a transformer, and the pairs of thyristors areprovided on the primary side of the transformer.

DESCRIPTION OF THE DRAWING The drawing schematically shows a circuitdiagram of an arrangement according to the invention.

DESCRIPTION OF SPECIFIC EMBODIMENT The following disclosure .is offeredfor public dissemination in return for the grant ofa patent. Although itis detailed to ensure adequacy and aid understanding, this is notintended to prejudice that purpose of a patent which is to cover eachnew inventive concept therein no matter how others may later disguise itby variations in form or additions or further improvements.

An a.c. voltage is applied to input connections 10, 12. To the extentthat the a.c. voltage is applied to the primary of transformer 14, thetransformer secondary applies it to a rectifier bridge 16. A storagecapacitor 18 is connected to the output of the rectifier bridge 16. Aflash tube 20 is ignited in a conventional manner by voltage from anignition transformer 24 applied to an ignition electrode 22. Uponclosing of a contact 26 (or a corresponding electronic arrangement) theignition transformer 24 receives a pulse from an ignition capacitor 28causing an ignition pulse across the ignition electrode 22. The storagecapacitor 18 then is discharged across the flash tube 20.

In the a.c. circuit on the primary side of transformer 14 are connecteda first pair of antiparallelly connected thyristors 30, 32. These areignited by an ignition device 34 of known type at the beginning of eachhalfperiod of the a.c. voltage, one being ignited during one half-waveand the other being ignited during the succeeding half-wave. Moreover,an auxiliary capacitor 38 is charged by the a.c. voltage via arelatively small charging resistor 36. The voltage across the auxiliarycapacitor 38 substantially follows the applied a.c. voltage. Referencenumerals 40 and 42 designate a second pair of antiparallelly connectedthyristors which are controlled by an ignition device 44. Upon ignitionof one of these thyristors of which, of course, only one ignites duringeach half-wave, the voltage of the capacitor 38 is connected behind thethyristors 30, 32 via a line 46, so that it is connected across thefirst pair of thyristors 30, 32 in opposition to the applied a.c.voltage. Therewith, the voltage applied to the thyristors 30, 32disappears, since the capacitor 38 is charged to the instantaneous valueof the applied a.c. voltage for all practical purposes. The thyristors30 and 32 therefore quench so that the current flux in the circuit ofthe transformer primary ceases. Thereupon, the further charging of thestorage capacitor 18 is interrupted.

A voltage divider comprising a fixed resistor 48 and an adjustableresistor 50 is connected in parallel with the storage capacitor 18.partial voltage of the voltage applied to the capacitor 18 is picked offacross the voltage divider 48, 50. This partial voltage controls theignition circuit 44 via a glow lamp S2 (i.e. a gas filled lamp having avoltage threshold at which it will commence conducting current). Thepicked-off partial voltage across the voltage divider 48, 50 is comparedwith the fixed threshold value of the glow lamp 52. By adjustment of theresistor 50 the voltage value across the capacitor 18 can be variedwithin wide limits, at which the glow lamp 52 ignites and in turnignites the thyristors 40, 42 via the ignition circuit 44 and causes thethyristors 30, 32 to be quenched. Thus, the thyristors 30, 32 areconnected in the meaning of a regulation by the voltage actually appliedacross the capacitor 18.

Thus, it is possible to charge the capacitor to an adjustable desiredvoltage, either once during each halfwave, for instance for astroboscopic flash illumination, or integratingly over a plurality ofhalf-waves for individual flash release. If, in the latter case, thevoltage of the storage capacitor 18 approximates the set-point value,the quenching point for each half-wave via the control unit 44 is movedincreasingly farther towards the beginning of each half-wave, so thatfinally, the further charging is interrupted.

Iclaim:

1. In an apparatus for charging a storage capacitor from alternatingcurrent provided at a.c. input connections, comprising a rectifier,first means connecting said connections to said rectifier, and secondmeans connecting said rectifier to said capacitor, the improvementcomprising: I

said first means including a first pair of antiparallel connectedthyristors in series between said connections,

a first ignition device connected to said thyristors to ignite themrespectively at about the start of each half cycle of the alternatingcurrent,

an auxiliary capacitor and a resistor connected in series between saidconnections so that the auxiliary capacitor is charged by the a.c.voltage during each half cycle,

a second pair of antiparallel connected thyristors,

a second ignition device connected to said second pair of thyristors toignite them respectively, arid means connecting said capacitor and saidsecond 'pair of thyristors across the first pair of thyristors inopposition to the a.c. voltage across the first pair of thyristors soupon ignition of one of the second pair of thyristors the capacitor isapplied across the first pair of thyristors to shut off the same.

2. In an apparatus as set forth in claim 1 including means connectingthe storage capacitor to the second ignition device for controlling theoperation of the second ignition device in response to t e charge in thestorage capacitor.

3. In an apparatus as set forth in claim 2, wherein said last mentionedmeans includes an adjustable voltage divider connected in parallel tothe storage capacitor, said voltage divider having a voltage pick-offconnection, and including threshold means connecting said pick-offconnection and said second device.

4. in an apparatus as set forth in claim 3, wherein said threshold meansis a glow lamp.

5. In an apparatus as set forth in claim 4, wherein said first meansincludes a transformer having a primary and a secondary, said rectifierbeing a bridge rectifier connected across said secondary, said firstpair of thyristors being in series with said primary.

6. In aii apparatus as set forth in claim 1, wherein said first meansincludes a transformer having a primary and a secondary, said rectifierbeing a bridge rectifier connected across said secondary, said firstpair of thyristors being in series with said primary.

7. In an apparatus as set forth in claim 2, wherein said first meansincludes a transformer having a primary and a secondary, said rectifierbeing a bridge rectifier connectcd across said secondary, said firstpair of thyristors being in series with said primary.

8. In an apparatus as set forth-- in claim 3, wherein said first meansincludes a transformer having a primary and a secondary, said rectifierbeing a bridge rectifi er connected across said secondary, said firstpair of thyristors being in series with said primary.

1. In an apparatus for charging a storage capacitor from alternatingcurrent provided at a.c. input connections, comprising a rectifier,first means connecting said connections to said rectifier, and secondmeans connecting said rectifier to said capacitor, the improvementcomprising: said first means including a first pair of antiparallelconnected thyristors in series between said connections, a firstignition device connected to said thyristors to ignite them respectivelyat about the start of each half cycle of the alternating current, anauxiliary capacitor and a resistor connected in series between saidconnections so that the auxiliary capacitor is charged by the a.c.voltage during each half cycle, a second pair of antiparallel connectedthyristors, a second ignition device connected to said second pair ofthyristors to ignite them respectively, and means connecting saidcapacitor and said second pair of thyristors across the first pair ofthyristors in opposition to the a.c. voltage across the first pair ofthyristors so upon ignition of one of the second pair of thyristors thecapacitor is applied across the first pair of thyristors to shut off thesame.
 2. In an apparatus as set forth in claim 1 including meansconnecting the storage capacitor to the second ignition device forcontrolling the operation of the second ignition device in response tothe charge in the storage capacitor.
 3. In an apparatus as set forth inclaim 2, wherein said last mentioned means includes an adjustablevoltage divider connected in parallel to the storage capacitor, saidvoltage divider having a voltage pick-off connection, and includingthreshold means connecting said pick-off connection and said seconddevice.
 4. In an apparatus as set forth in claim 3, wherein saidthreshold means is a glow lamp.
 5. In an apparatus as set forth in claim4, wherein said first means includes a transformer having a primary anda seconDary, said rectifier being a bridge rectifier connected acrosssaid secondary, said first pair of thyristors being in series with saidprimary.
 6. In an apparatus as set forth in claim 1, wherein said firstmeans includes a transformer having a primary and a secondary, saidrectifier being a bridge rectifier connected across said secondary, saidfirst pair of thyristors being in series with said primary.
 7. In anapparatus as set forth in claim 2, wherein said first means includes atransformer having a primary and a secondary, said rectifier being abridge rectifier connected across said secondary, said first pair ofthyristors being in series with said primary.
 8. In an apparatus as setforth in claim 3, wherein said first means includes a transformer havinga primary and a secondary, said rectifier being a bridge rectifierconnected across said secondary, said first pair of thyristors being inseries with said primary.